It looks to me like when a skin generates an empty bloglist, the b2evolution engine (or something that it uses) generates invalid XHTML:

Code

<ul id="bloglist"></ul>

The XHTML validator complained about this:

Error Line 32 column 22: end tag for "ul" which is not finished.
<ul id="bloglist"></ul>
Most likely, You nested tags and closed them in the wrong order. For example <p><em>...</p> is not acceptable, as <em> must be closed before <p>. Acceptable nesting is: <p><em>...</em></p>

Another possibility is that you used an element which requires a child element that you did not include. Hence the parent element is "not finished", not complete. For instance, <head> generally requires a <title>, lists (ul, ol, dl) require list items (li, or dt, dd), and so on.